Irradiation induced lattice defects in Si1-xGex devices and their effect on device performance

A study is presented of the nature and influence on device performance of lattice defects in strained n+-Si/p+-Si1-xGex epitaxial diodes and n+-Si/p+-Si1-xGex n-Si epitaxial heterojunction bipolar transistors introduced by fast neutrons and MeV energy electrons. The generation of deep levels in the strained Si1-xGex epitaxial layers and the degradation of device characteristics are also reported as a function of fluence and germanium content. The degradation of device performance of both diodes and heterojunction bipolar transistors by irradiation increases with increasing fluence, whereas it decreases with increasing germanium content. For x = 0.12 diodes irradiated by 1 MeV electrons, hole and electron capture levels are induced in the Si1-xGex epitaxial layers, although electron capture levels only are formed for x = 0.16 diodes. For x = 0.12 diodes irradiated by 1 MeV fast neutrons, only electron capture levels are induced. Based on the annealing behaviour of the electrical characteristics and of the lattice defects, it is concluded that the electron capture levels, which are related to interstitial boron, are mainly responsible for the increase of reverse and forward current in 1 MeV electron irradiated diodes. (Author)